Electrochemistry

OIL RIG Electrochemistry Oxidation is loss (of e-) Reduction is gain (of e-)

LEO the lion goes GER Lose electrons = Oxidation Gain electrons = Reduction

Balancing Acidic Reactions Split the reaction into two halves Balance the common element on the two sides. Balance the Oxygen by adding water to the opposing side Balance the hydrogen by adding H+ ions to the opposing side Balance the overall charge by adding electrons

Redox Reactions in Acid Al + MnO4-1  Al3+ + Mn2+

MnO4-1+ Fe2+  Fe3+ + Mn2+

Cr2O7-2 + HNO2  Cr+3 + NO3-1

C + H+ + SO42-  CO2 + SO2

Basic Redox Calculate the charge of P in PO4-3 Calculate the charge of Cr in Cr2O7-2

Steps Split into two half reactions Balance the common ion Balance the charge of the common ion by using electrons Balance the overall charge by using OH- Balance the hydrogen by adding H2O

Balancing Basic Redox Reactions Break into two halves Balance common element Balance Oxygen by adding water to opposing side Balance hydrogen by adding H+ ions to opposing side Balance overall charge by adding electrons Get rid of H+ by adding OH- to both sides (H + OH = H2O). Cancel out waters from both sides. Find least common multiple of electrons Combine two halves.

Redox Reactions in Basic Solutions Mg + OCl-  Mg(OH)2 + Cl-

Cl- + Cr2O7-2  Cr3+ + ClO2-

PbO2 + SeO32-  PbO + SeO42-

MnO4- + NH3  NO3- + MnO2

Electrochemistry Study of the flow of electrons Study of electricity Powered by Redox reactions

OIL RIG Electrochemistry Oxidation is loss (of e-) Reduction is gain (of e-)

LEO the lion goes GER Lose electrons = Oxidation Gain electrons = Reduction

An Ox and a Red Cat Cathode – where reduction takes place (GER) Red Cat (Reduction at the Cathode) Anode – where oxidation takes place (LEO) An Ox (Anode has Oxidation)

FAT CAT Electrons travel From Anode To CAThode in a voltaic or electrolytic cell

Electrolytic Cells vs. Voltaic Cells A cell which contains a nonspontaneous reaction caused by passing a current through the solution Example: solution with wire connecting the two Galvanic or Voltaic cells, are done by spontaneous reactions Example: batteries

In one beaker, there is a solution of Iron (II) with an iron electrode immersed in the liquid. A second beaker contains a solution of Cadmium (II) with a cadmium electrode immersed into the liquid. The two beakers are connected by a salt bridge, and the following reaction takes place. Fe + Cd2+  Fe2+ + Cd

A solution of Cu2+ with a Cu electrode and a solution of Zn2+ with a Zn electrode. The Cu electrode is becoming bigger while the Zn electrode is becoming smaller.

A solution of sodium chloride and water has a current passed through it. As the current flows through the container, hydrogen gas begins to form on one electrode, while chlorine gas begins to form on the other.

Starter 4/28/14 1) Pick up a white board, eraser, and Expo (***DO NOT WASTE THE EXPO DRAWING RANDOM THINGS***) 2) Get out homework of Electric Cells 3) KEEP HW on your desk but clear desk of everything else. All you need is: Whiteboard Expo Eraser HW: Electric Cells

Spontaneity of the Reaction If E is positive the reaction is _____________ If E is negative the reaction is ____________

Cu + Zn2+  Cu2+ + Zn

Na+ + H2O  Na + O2

Electroplating 1 mole of e- = 96485 Coulombs Amperes = Coulombs/sec

Remember If solving for Amps, that is equal to Coulombs per second. Solve for Coulombs and then divide by the number of seconds

Calculate the mass of Copper metal produced during the passage of 12 Calculate the mass of Copper metal produced during the passage of 12.5 amperes through a solution of copper (II) sulfate for 30 minutes

What volume of Oxygen (at STP) is produced by the oxidation of water in electrolysis of copper (II) sulfate in the previous example.

Calculate the amount of time required to produce 2000 grams of magnesium metal by electrolysis of molten MgCl2 using a current of 75 A.

A Cr3+ solution is electrolyzed, using a current of 17. 60 A A Cr3+ solution is electrolyzed, using a current of 17.60 A. What mass of Cr is plated out after 1.50 days?

What amperage is required to plate out 24 What amperage is required to plate out 24.6 grams Cr from a Cr+3 solution in a period of 2.8 hours?